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Steam boilers are essential in manufacturing and process industries. However, they also have the potential to explode. Water is essential for the production of steam, but it can also be a factor that damages boiler systems. Low water levels are a leading cause of boiler accidents. To ensure safe boiler operation, it is important to maintain the water level. The steam boiler will experience low-water conditions when the water level in the boiler drum falls below the low-water mark. This can cause severe damage to the boiler.

What does low water level mean in steam boilers?

Low water levels in steam boilers occur when the water falls below the lowest mark of water or even the top of tubes. This causes the tubes to heat up. The steel may be damaged if the water level falls below the main firing tubes. It can be avoided with regular steam boiler maintenance.

Steel strength is significantly reduced at temperatures over 800degF (480degC) as the temperature of the furnaces generally exceeds 1,800degF. Low water levels can cause steel tubes to melt. Water flashes into steam as it enters a boiler that is overheated. Due to the sudden pressure increase, metal parts that are impacted rupture and cause a steam blast.

Effects on Steam Boiler Low Water Level:

The steam boiler is already overheated, so adding water to it is a very dangerous situation. The water will quickly become steam, which can lead to a huge pressure and explosion in the steam boiler. This is one of most dangerous outcomes for any boiler and should be avoided.

Damage commonly caused by low water levels is:

  • Tubes that are not tightly coiled
  • Crack tubes
  • Melting metal
  • Leaking water

Controlling Water Drum Level:

The water level of a boiler drum can be difficult to control, as it is a mixture of water and bubbles, which shrink and expand with pressure changes. As the steam demand increases, the pressure inside the boiler decreases. This causes the water level in the drum to rise. As the freshwater from the feed tank cools the drum, the steam bubbles collapse and the water level drops. A three-level drum control is the solution to the shrink and swell in the steam boiler.

Operator and equipment problems can cause low water levels. Common causes of low water levels include:

  • Failure of the feedwater pump
  • Control valve failure
  • Water loss in the deaerator system or make-up water systems
  • Failure of the drum level controller
  • Drum level controller in manual position
  • Air pressure loss at the valve actuator
  • Safety valve Lifting
  • Steam load changes dramatically and suddenly

Low Water Cutoff:

Low water cutoffs are installed on steam boilers to prevent damage. The device detects low water and shuts down the boiler system. The burner is not activated until the water level returns to normal.

Some low-water cutoff devices have the dual purpose of stopping and starting the feedwater flow as well as stopping the burner. This device is called the Primary Low Water Cutoff. The Secondary Low Water Cutoff device is also used to initiate a safety lockout and shutdown.

Failures of Low Water Cutoff Devices:

Low Water Cutoff Devices work well and are reliable. The following factors may cause a failure.

Deposits Condensate and new make-up waters enter a steam boiler to deposit minerals and solids.

Outdated Models Most boiler manufacturers recommend replacing the mechanical components in the steam boiler system on a regular basis. If outdated boilers are not replaced, they can cause leaks and part failure.

Water Loss: Steam leaks, faulty steam traps that require a large amount of makeup water can cause problems in steam boilers. Low Water Cutoff devices are also affected by water loss. The entire system must be maintained in such cases.

Jumpers : Sometimes, jumper cables are used to diagnose a problem temporarily or bypass a circuit during testing. The Low Water Cutoff Device will not shut down the burner if it is ignored.

Maintenance Proper boiler maintenance requires the purging of Low Water Cutoff Device System. This requires care as incorrect flushing can cause damage.


Veda is a leading boiler manufacturer and combustion expert in the world. We specialize in thermal solutions. Our steam boilers, boiler accessories and design experience spans more than 20 year. Veda provides a wide range of high quality steam boilers compatible with different fuels and applications.